This problem only happens when the RichTextBox is hosted inside a RadWindow.  It is fine when it is embedded in a normal page.

If you have browser zoom (bottom right for IE 8) set to something not 100% (e.g. 125%), then the caret position does not reflect the cursor position.  For example, with 125% if you try to highlight a line, you will see that the cursor is on line 1 but the caret position and text highlighted is on line 3.

Version tested are SL4 2012.2.725 and 2012.2.912.  I hope there is a solution that does not involve upgrading to a SL5 only build.

Hi Edward,

Thank you for your question.

Incorrect caret positioning problem when RadRichTextBox is used in RadWindow and zoomed browser is resolved for Silverlight 5 version of our assemblies. Unfortunately, the only solution for you could be to upgrade your project to Silverlight 5. Otherwise, as a workaround you could use the zoom functionality of RadRichTextBox to zoom in/out its content instead of zooming the browser.

I hope this information helps. Please, do not hesitate to contact us if you need further assistance.

Regards,
Vasil
the Telerik team